In building construction it is sometimes necessary to build in accordance with a curved pattern in a region which is difficult to work in. For example, interior designers or architects sometimes design ceilings, floors or entire buildings having curved features. Construction of a curved ceiling (for example) typically requires that curved segments be cut into the ceiling, or that curved projections be constructed to project downwardly from the ceiling. The designs are normally defined in terms of circles or arcs having prescribed radii.
There are several prior art techniques for constructing circular or curved ceilings. One prior art technique is to build a large mechanical compass capable of scribing circles or arcs of the desired radius. The compass is used to mark the prescribed circles or arcs on easily cut material such as paper, which is then cut into the required shape(s). The cut piece(s) are temporarily applied to the ceiling to serve as a guide to the construction of the required curved indentations and/or projections on the ceiling. If the room is not big enough to accommodate the mechanical compass then the marking and cutting is done in a warehouse or other space large enough to accommodate the compass. The cut pieces are transported to the job site, and applied to the ceiling as aforesaid. Canadian Patent No. 693,273 issued 25 Aug., 1964 for an invention of Michelle Quenot entitled "Instrument for Tracing Circles" discloses one type of mechanical compass capable of scribing large radius circles or arcs as aforesaid.
An alternative prior art technique for constructing circular or curved ceilings is to use a large mechanical compass to scribe the required circles or arcs onto the floor of the room in question. A plumb bob is then used to project points on the floor pattern up to the ceiling. The ceiling points are then connected, yielding the desired curved pattern on the ceiling. Workers then use the ceiling pattern as a guide to form the necessary curved indentations and/or projections on the ceiling.
The prior art techniques aforesaid are subject to a number of disadvantages. They require painstaking effort and accuracy which is difficult to achieve in a congested, cramped workspace such as a room undergoing construction. Accurate reproduction of the prescribed circular or curved ceiling design is typically a difficult, cumbersome, inefficient, labour-intensive, error-prone task. The present invention employs a laser to project a circle directly onto a ceiling. The diameter of the circle can easily be adjusted. The worker is thus rapidly and efficiently provided with an accurate reference on the ceiling itself, which serves as a guide to the accurate formation of complex curved projections and/or indentations on the ceiling with relative ease.
The invention also facilitates accurate, efficient construction of cylindrical or conical-shaped structures such as clarifiers, silos, hoppers and the like. It can be a difficult, time-consuming, cumbersome operation to ensure that the cylindrical (or conical) portions of such structures have a uniform circular cross-section (or a uniformly increasing or decreasing circular cross-section). By using the present invention to project circles of known, accurate diameter directly onto any desired portion of the structure during its construction, the construction supervisor may easily ensure that the required circular cross-section is maintained (or uniformly varied) throughout the construction project.
In the prior art, lasers have been used in building construction to produce reference lines on walls as an aid to accurate construction. For example, the LaserLevel.TM. device produced by Spectra-Physics Construction and Agricultural Division of Dayton, Ohio produces a pencil-thin beam of visible red laser light. The beam is rotated 360.degree. to project a continuous, visible horizontal or vertical reference line on the walls of a room. The visual reference line may be aligned with any desired reference, and may be used as a guide for the installation of acoustical ceilings, computer floors, raised access flooring, partitions, drywall, etc. However, no provision is made for redirecting the beam to yield a pattern such as a circle on a wall, floor or ceiling.
The prior art discloses various techniques for using light sources to illuminate patterns as a guide to construction. Canadian Patent No. 608,007 issued 1 Nov., 1960 for an invention of Slater et al. entitled "Method and Means for Marking Out Work" uses an optical system to project light through a patterned template to produce an enlarged shadow on a workpiece. The shadow serves as a guide to construction. This technique requires painstaking effort in reducing the size of the pattern and accurately cutting the template.
U.S. Pat. No. 4,693,567 issued 15 Sept., 1987 for an invention of Yasuto Ozaki entitled "Apparatus for Projecting Luminous Lines on an Object by a Laser Beam" employs a pair of convex and concave lenses together with a specially shaped reflector to deflect a laser beam onto a surface, yielding a pattern governed by the shape of the reflector. A drawback of Ozaki's device is that different reflectors are apparently required to yield different patterns. Accordingly, Ozaki's device seems to be restricted, as a practical matter, to use in situations in which the effort and expense of constructing a special reflector can be justified.